Seats, galleys, monuments and tie downs in an aircraft usually are connected to the aircraft via seat rails that extend in a longitudinal direction (i.e. X-direction) through the aircraft and that are attached to cross beams, which extend in a transverse direction (i.e. Y-direction) to stabilize frames that surround the aircraft and which may be supported by vertical struts.
The struts, crossbeams, frames, ribs, stringers, floor and the skin of the aircraft are part of a so-called primary structure, which provides the elements for stiffing the overall structure of the aircraft. For example, the cross beams reinforces the frame against inner pressure which leads to tension stresses and classifies it as a primary structure part. The floor creates the shear stiffness for the fuselage. For example, together with the other parts of the primary structure, the cross beams are tested under the full fatigue spectra in the major fatigue test.
Other elements of the aircraft, such as, for example, lashing brackets are part of a so-called secondary structure and are also used to install the equipment like seats, monuments, galleys, toilets, etc. The floor may work like a big shear web, which may distribute all equipment loads in flight direction directly over its side attachment to the skin. The distribution of the loads may be driven by stiffness. Usually, the seat rails are used for mechanically decoupling the secondary structure from the primary structure. The seat rails may be seen as load distribution elements for seat loads into the floor panels.
U.S. Pat. No. 7,462,006 A1 and DE 10 2007 011 611 A1 show a fastening arrangement for lashing brackets in the floor of a cargo hold of an aircraft. The connection between a lashing bracket and a frame of the aircraft is performed with two half-barrel nuts.
Other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.